Field of the Invention
The present invention relates to a vehicle steering system, and particularly relates to a vehicle steering system for assisting steering of a steering wheel such that a vehicle travels following a desired target traveling line.
Description of the Background Art
There has hitherto been known a technique of assisting steering of a steering wheel or performing automatic steering such that a vehicle travels following a desired target traveling line.
For example, as disclosed in Japanese Patent Application Laid-Open No. 2015-13545, there is a technique of recognizing a white line on a road by using a camera attached to the front of a vehicle, to perform steering control such that the vehicle travels at the center of a lane. This is called a lane keeping system.
Further, as disclosed in Japanese Patent Application Laid-Open No. 2005-67484, there is a technique of calculating a target trajectory by obtaining a subject vehicle position, a target point preset by the driver, map data, and the like based on satellite information, to perform steering control such that the vehicle follows the target trajectory.
However, in the conventional techniques disclosed in Japanese Patent Application Laid-Open Nos. 2015-13545 and 2005-67484, when the driver deviates from the target traveling line and performs steering intervention, i.e., so-called override, in which the driver operates the steering wheel so as to avoid other vehicles, obstacles, and the like on the target traveling line, large steering assist force is instantaneously generated for canceling the deviation from the target traveling line due to the override, and interferes with the driver's steering intervention, thereby causing a problem that the operation of avoiding other vehicles, obstacles, and the like is inhibited.
In contrast, for example, Japanese Patent Application Laid-Open No. 10-152063 (1998) discloses a technique of detecting the driver's steering intervention from steering force which is the steering state of the steering wheel, to make corrections so as to reduce a control amount of the lane keeping system.
Moreover, Japanese Patent Application Laid-Open No. 2015-33942 discloses a technique of calculating a risk level based on information relating to the safety of traveling, acquired from a known in-vehicle control system and vehicle-mounted sensor such as the driver's steering intervention, a stop control execution request flag by a PCS (pre-crash system), rain determination by a rain sensor, and brightness determination by an illuminance sensor, to make corrections so as to reduce a control amount of the lane keeping system in accordance with the risk level.
In Japanese Patent Application Laid-Open Nos. 10-152063 (1998) and 2015-33942, a correction coefficient of the steering control amount of the lane keeping system, which is a vehicle steering device, is calculated based on a steering angle being the steering state of the steering wheel or an instantaneous value of steering torque by using a map or a table, to make corrections so as to reduce the control amount when the driver performs override. However, after the decrease in the control amount due to the driver's steering intervention and immediately after completion of the steering intervention, that is, immediately after completion of the override, the control amount abruptly increases, thereby causing a problem that, in some cases, the vehicle fluctuates at the time of control-switching and smooth control-switching cannot be performed.